How to set Chrome preferences using Selenium Webdriver .NET binding?

Question

Here is what I'm using, user agent can be successfully set, while download preferences cannot.

Windows 7, Chrome 26, Selenium-dotnet-2.31.2, chromedriver_win_26.0.1383.0

ChromeOptions chromeOptions = new ChromeOptions();
var prefs = new Dictionary<string, object> {
    { "download.default_directory", @"C:\code" },
    { "download.prompt_for_download", false }
};
chromeOptions.AddAdditionalCapability("chrome.prefs", prefs);
chromeOptions.AddArgument("--user-agent=" + "some safari agent");
var driver = new ChromeDriver(chromeOptions);

Taken from chromedriver.log:

[1.201][FINE]:      Initializing session with capabilities {

   "browserName": "chrome",

   "chrome.prefs": {

      "download.default_directory": "C:\\code",

      "download.prompt_for_download": false

   },

   "chrome.switches": [ "--user-agent=Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/534.57.2 (KHTML, like Gecko) Version..." ],

   "chromeOptions": {

      "args": [ "--user-agent=Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/534.57.2 (KHTML, like Gecko) Version..." ],

      "binary": "",

      "extensions": [  ]

   },

   "javascriptEnabled": true,

   "platform": "WINDOWS",

   "version": ""

}

Check the temp Preferences file at *temp\Google\Chrome\User Data\Default\Preferences, no "default_directory" and "prompt_for_download" are set.

   "download": {
      "directory_upgrade": true
   },

Answer 1

If you have updated to Chrome Version 36.0.x and Selenium 2.42, Martins solution no longer works.

It seems to have been updated. You now can use the following code

ChromeOptions options = new ChromeOptions();
options.AddUserProfilePreference(string preferenceName, object preferenceValue); 

I currently use it to change my Printer settings to "Save as PDF" instead of the default using this code as an example

ChromeOptions options = new ChromeOptions();
options.AddUserProfilePreference("printing.print_preview_sticky_settings.appState", "{\"version\":2,\"isGcpPromoDismissed\":false,\"selectedDestinationId\":\"Save as PDF\");

I thought Martin's solution was very good and accurate, but it suddenly stopped working for me, so naturally I had to see if I could find a solution.